Atherosclerosis is a disease that is characterized by irregularly distributed lipid deposits, called plaque. Plaque is deposited in the lumen or central portion of large and medium-sized arteries and results in a narrowing of the lumen. Atherosclerosis usually occurs in the second or third decade of life and typically affects the entire length of the coronary artery in varying degrees. In some portions of the coronary artery, the arterial lumen exhibits a more severe narrowing called "stenosis." When the stenosis severity reaches across 75-80% of the cross sectional area of the artery, symptoms of myocardial ischemia, the inadequate circulation of blood to the myocardium, the muscular layer of the heart, occur. Myocardial ischemia is sometimes accompanied by angina pectoris, a severe constricting pain in the chest radiating from the chest into the shoulder and down the left arm. Also attendant with the progression from stenosis to total occlusion of the coronary artery are coronary spasms and the formation of intraluminal coronary thrombi or blood clots.
Plaque consists of acellular fibrous tissue, calcified tissue and amorphous debris that includes cholesterol clefts containing extra-cellular lipid, called pultaceous debris. It is known that plaque morphology varies as a function of cross-sectional narrowing of the artery. That is, the amount of plaque increases as the severity of stenosis increases and at times, produces total occlusion of the coronary artery that requires reconstructive revascularization by the traditional method called coronary transluminal angioplasty.
Percutaneous transluminal coronary angioplasty (PTCA), using a balloon catheter was first introduced in the mid-1970's and has become one of the recognized methods for treating obstructed coronary arteries. The procedure is generally performed by making a needle puncture in the patient's groin to gain access to the femoral artery and a sheath or introducer is inserted into the wound. A guidewire is passed through the sheath and routed through the vascular system until the distal end of the wire reaches the coronary ostium, the opening from the ascending aorta into the coronary artery. A guiding catheter is next advanced over the guidewire until its distal end exits over the distal end of the guidewire. A special PTCA wire is then advanced through the guiding catheter into the proximal coronary stump, the area between the ostium and the occlusion, up to the origin of the total occlusion. The physician, by manipulating the proximal end of the wire, attempts to pass it across the stenotic lesion that is obstructing the artery. If the physician successfully manipulates the guidewire past the stenotic lesion, a PTCA balloon angioplasty catheter is passed over the guidewire by feeding the distal end of the balloon catheter over the proximal end of the guidewire and then pushing the balloon catheter over the guidewire until the balloon is adjacent to the stenotic lesion. In position, the balloon is inflated to press the occlusion against the wall of the artery thus restoring patency to the artery.
Frequently, however, the traditional method of transluminal angioplasty using a balloon catheter is not successful because it depends on the ability to insert the guidewire through the stenosis. If the stenosis is so dense that the guidewire cannot be inserted through it, the balloon catheter will also not be able to pass through the stenosis. Rather, the balloon can only be advanced up to the tip of the wire, just outside the occlusion, and then inflated. In this case arterial patency will not be restored.
Another problem associated with the traditional method is due to the fact that total occlusions frequently occur very close to the ostium. Thus, a very short area in which the physician may manipulate the balloon is provided ( the "coronary stump"). PTCA balloons are commercially available in lengths of at least two centimeters. If the balloon is inflated in a coronary stump of less than two centimeters, it may displace the guiding catheter away from the occlusion and into the arterial wall and the balloon may tear.
In addition, conventional balloon catheters have tapered oval ends with a shaft tip extending three to five millimeters beyond the distal portion of the balloon. If the physician is unable to direct the shaft tip to the ideal location relative to the total occlusion, the tip may bend thereby reducing the extent to which the physician may advance it further into the artery. Furthermore, the shaft tip prevents the balloon from entering the most proximal portion of the total occlusion. If the balloon cannot enter the occlusion, it cannot be inflated directly adjacent to the total occlusion. This reduces the chances of restoring patency to the totally occluded artery.
A tapered balloon has the added undesirable effect of allowing the arterial wall in the area adjacent to the total occlusion to recoil, which prevents the development of a cleft. Cleft formation during percutaneous transluminal angioplasty is desirable because it provides the pathway through which the guidewire may be inserted across the total occlusion. This in turn enhances the successful completion of the procedure.
The success rate of the conventional method is further mitigated by abrupt total occlusion of the artery without tapering, total occlusion of the artery of greater than six months duration, stenotic lesions greater than three centimeters in diameter, and occlusion that is flush at the ostium of the vessel that allows no stump with which to start the procedure.
Objects and advantages of the present invention in achieving these and other goals will become apparent from the following descriptions, taken in connection with the accompanying drawings, wherein are set forth by way of illustration and example certain embodiments of the present invention.